Thursday, April 10, 2008

Indian River Tern or just River Tern (Sterna aurantia) is a bird in the tern family . It is a resident breeder along inland rivers from Iran east through Pakistan into India and Myanmar to Thailand, where it is uncommon. It does not occur in Sri Lanka. Unlike most Sterna terns, it is almost exclusively found on freshwater, rarely venturing even to tidal creeks.
This species breeds from March to May in colonies in less accessible areas such as sandbanks in rivers. It nests in a ground scrape, often on bare rock or sand, and lays three greenish-grey to buff eggs, which are blotched and streaked with brown.
This is a medium-sized tern, 38-43 cm long with dark grey upperparts, white underparts, a forked tail with long flexible streamers, and long pointed wings. The bill is yellow and the legs red. It has a black cap in breeding plumage. In the winter the cap is greyish white, flecked and streaked with black, there is a dark mask through the eye, and the tip of the bill becomes dusky.
The sexes are similar but juveniles have a brown head, brown-marked grey upperparts, grey breast sides and white underparts. The bill is yellowish with a dark tip
As with other Sterna terns, the River Tern feeds by plunge-diving for fish, crustaceans, tadpoles and aquatic insects in rivers, lakes, and tanks. Its numbers are decreasing is due to the pollution of their habitat.
It is a slender, graceful, grey and white tern with long, deeply forked 'shallow' tail. It has a deep yellow bill and short red legs. In summer, entire forehead, crown and nape appear glossy jet black in color. In winter, it is greyish white flecked and streaked with black, especially on nape. Both sexes are alike. It lives gregariously, on rivers and jheels, flying up and down. It flies a few feet above water with deliberate beats of the long, slender, pointed wings intently scanning the surface for fish venturing within striking depth. From time to time, it plunges in with closed wings, often becoming completely submerged but soon reappearing with the quarry held across the bill. As it resumes its flight, the victim is jerked up in the air and swallowed head foremost. In addition to fish, crustaceans, tadpoles and water insects are also eaten by the bird. The Indian River Tern's nesting season is chiefly from March to May. The eggs are laid on bare ground on sandbanks of large rivers in colonies.

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